Kieran Culkin admits to getting Mark Ruffalo high on stage during their Broadway run of The Moment When

Kieran Culkin confesses to a prank he pulled on his former Broadway co-star Mark Ruffalo almost 25 years ago.

The 42-year-old actor was just 17 when he starred in a 2000 production of James Lapine’s The Moment When.

In one scene, Ruffalo was called upon to roll and smoke a fake joint, with Culkin revealing that there was a “bag of fake joints,” and he swapped one for a real one.

“I was seventeen and stupid,” Culkin admitted, adding that weeks later he smelled marijuana and knew that the real joint, as it turned out, had been found on stage by Ruffalo.

He added that he “just watched” as Ruffalo took long, extended drags of what he thought was fake marijuana.

“I’m like, ‘I thought this was a good joke. I’m stupid. Oh my God, I’m so sorry.’ But actually they loved it,” Culkin admitted.

In one scene, Ruffalo was called upon to roll and smoke a fake joint, with Culkin revealing that there was a “bag of fake joints,” and he swapped one for a real one.

“Mark says, ‘I haven’t smoked weed in ten years; the second half is going to be so fun,’” Culkin added.

He said there was another co-star, “who had never smoked weed in her life,” who said, “Is this what being high is?” This is beautiful.’

“And then Phyllis Newman comes in and says, ‘I haven’t smoked weed since the ’60s. Thank you, honey,'” Culkin said, though he admitted the director wasn’t too happy.

“Then the director comes rushing in and says, ‘I don’t care who it is, or what happened, but Kieran, give me the joint,’” he recalled.

“I sheepishly handed her the cockroach and she said, ‘Ruin your life on your own time,'” Culkin added.

Ruffalo previously spoke about the incident in 2012 during an appearance on The Graham Norton Show, although he did not name Culkin as the culprit.

“There was a play I did where I had to smoke a joint in the first scene. And of course there was a very mischievous young actor I was in the play with who, on opening night, along with all the critics, popped a real joint on the table,” Ruffalo said.

He admits that he tends to “overdo everything” when he’s on stage, explaining that he inhales very large amounts of what he thought was fake weed.

“Mark says, ‘I haven’t smoked weed in ten years; the second half is going to be so fun,’” Culkin added.

He said there was another co-star, “who had never smoked weed in her life,” who said, “Is this what being high is?” This is beautiful’

“Then the director comes rushing in and says, ‘I don’t care who it is, or what happened, but Kieran, give me the joint,’” he recalled.

‘And the little boy who put the joint on the table is standing there, [laughing]. And I just said, “Oh shit,” he said

‘The two of us smoked a huge blunt on stage. And I thought, ‘Man, I’m in it tonight. I feel it. I’m on fire. I feel it… why is that guy backstage laughing at me?'” Ruffalo said.

‘And the little boy who put the joint on the table is standing there, [laughing]. And I just said, “Oh shit,” he said.

“But at the end of the play I got the best reviews of my entire career,” Ruffalo said, although he admitted it was a “nightmare experience” and that he would “never do that again.”

Culkin is currently receiving critical acclaim for his performance in A Real Pain and he returns to Broadway this spring in a revival of Glengarry Glen Ross.